Influence of chisel edge thinning on helical point micro-drilling performance

Chisel edge thinning can effectively improve the drilling performance of austenitic stainless steel. Four kinds of helical point micro-drills, each with a thinned chisel edge of a distinct length, are fabricated based on the mathematics models of the micro-drill by using a six-axis computer numerical control tool grinder. Micro-drilling experiments on 304 stainless steel are conducted. Drilling performance is evaluated according to the measured and observed micro-hole machining quality, chip morphology, thrust force, and tool wear of the micro-drill tip. With a decrease in the chisel edge length, the micro-holes drilled using thinned micro-drills have small entrance burrs, roundness errors, and regular shapes, which are attributed to an increase in self-centering capability. Owing to increased equivalent chip thickness and different directions of chip flow, micro-drills with thinned chisel edge can generate more small-size chips and improve chip breaking. In addition, the inner cutting edge with a positive rake angle replaces the chisel edge with a negative rake angle to cut the workpiece, significantly reducing the chip curl, thrust force, and tool wear of micro-drills. However, helical point micro-drills with critical chisel edge lengths by thinning exhibit less thrust force and tool wear than do helical point micro-drills with no chisel edge because of the increase in the uncut chip width of the micro-drill. Thus, with the selected parameter range, the optimal helical point micro-drill is the micro-drill with a specific chisel edge length by thinning to improve drilling performance.